For example, according to US2005/0083045A1 (JP-A-2005-10093), a liquid level detecting device includes a float, which floats in fluid to detect a liquid level of the fluid. The float is connected with one end of an arm. The arm is rotatably supported by a body at the other end. The other end of the arm is fixed with a magnet. The body has a magnetoresistive element as a magnetism detection element opposed to the magnet. The float moves correspondingly to change in a liquid level, so that the movement of the float is converted into a rotary motion of the arm, thereby the magnet rotates in conjunction with the liquid level. Thus, magnetic flux generated by the magnet rotates, so that the amount of the magnetic flux, which passes through a magnetoresistive element changes. The liquid level detecting device detects the liquid level in accordance with a signal level output from the magnetoresistive element, the signal level changing correspondingly to the change in the magnetic flux.
In the present structure, the magnet is fixed to a magnet holder. The body has an axis portion fitted to a hole of the magnet holder, so that the magnet holder is rotatable around the axis portion as a rotation axis relative to the body. That is, the hole of the magnet holder and the axis portion of the body construct a slide bearing and a slide axis.
In the present structure of the liquid level detecting device, the magnet holder and the body are immersed in fluid when the liquid level is high. In this condition, fluid infiltrates into a gap in a fitting portion between the magnet holder and the body. When the magnet holder rotates, the fluid infiltrating into the gap exerts frictional force to the fitting portion between the hole of the magnet holder and the axis portion of the body. When the fluid is low-viscosity fluid such as fuel for a motor vehicle, the frictional force is low even in a condition where the fluid infiltrates into the gap in the fitting portion. In this case, the magnet holder rotates promptly to change in the liquid level. Namely, the liquid level detecting device is quick in response to change in the liquid level. By contrast, when the fluid is high-viscosity fluid such as lubricating oil for a motor vehicle, high frictional force is exerted to the fitting portion between the hole of the magnet holder and the axis portion of the body when the magnet holder rotates. Accordingly, the magnet holder hardly rotate promptly to change in the liquid level, and consequently response in the liquid level detection may be impaired.